A light emitting diode (LED) is a semiconductor light emitting device that converts a current into light.
A wavelength of the light emitted from the LED varies depending on a semi-conductor material used for fabricating the LED. That is, the wavelength of the light depends on a band-gap of the semiconductor material, which is an energy difference between electrons in the valence band and electrons in the conduction band.
As the luminance of the LED has gradually increased, the LEDs have been widely used as light sources of a variety of devices such as display devices, vehicles, and lightings. In addition, it is also possible to realize high efficiency LEDs that can emit white light by combining LEDs having different colors or by using phosphor materials.
In order to apply the LEDs to the above purposes, the LEDs have to have excellent light emitting efficiency and excellent luminance.